Here several configs can be made, e.g. Platform Setup -> Choose RAM size for the right RAM size, or Environment -> Default kernel command line change the default kernel command line.
Close the menuconfig with 2x[ESC].

After you have saved the new .config, bootloader can be compiled:

make

When the process has completed successfully, a soft link to the apex.bin(the bootloader) is located in the same directory.

Now the bootloader only needs to be copied to the SD card as shown in the next section.

Copying the bootloader

sudo dd if=/dev/zero of=/dev/<partition of the bootloaders>

sudo dd if=apex.bin of=/dev/<partition of the bootloaders>

Which partition is the bootloader

If you are unsure which one is the right partition on the SD-Card you just follow these instructions:

sudo gparted

Then gparted is starting and top right you see the possible devices. If you have a 2GB SD-Card it looks like this:

Usually there are two partitions on the SD-Card. One for the Rootfs and one for the bootloader. The filesystem for the partition of the bootloader always displays unknown In this case the partition sdd2.

So, to copy the bootloader onto the SD-Card in this case you must proceed as follows: